Add the Ability to:
-Invade Countries, just like how you get invaded, and make a Map for each Superpower to invade
-Nuke other Countries: You can only sadly keep nukes to not get invaded, or to flex your muscles, you should be able to nuke other countries, so they can't do anything against you for 2-8 years.
-Attack Helicopters: Remember those Fire Helicopters? Well, you should also add Attack Helicopters, which are able to fire MGs and fire Rockets.
-Longer Bridges, and Bridge Customization: The bridge length limit is kind of stupid, you should be able to build longer Bridges, and also you should be able to customize them.
-New Research Ability: Build a platform on Water to build a city on: Costs 10.000 Knowledge, and gives you the Ability to build Platforms to build on Water, and to build a city on those Platforms.
-Ability to save Multiplayer Games: The Reason almost no one plays Multiplayer is because you can't save the game. You should be able to save.
-Ideologies: You should add Democracy (Gives Elections, etc.), Socialism (Equal Payment for all, etc.), and Imperialism (Ability to find new Islands and colonize them, if the Map thingy gets added, etc.).
-Power of the Nuke: The ability to give Nukes more power to devastate the Countries even more, but at a more expensive cost of Research and Money. Or decrease the power, to get it cheaper, but less effect.
-Weapon Designs: Make new weapon designs, for Guns, Tank, Artillery (We get to that later), Planes and Helicopters.
-Artillery: Effective when far away from enemies, but weak when to close. Also Artillery only in Tropico 6 would be fun.
Well, that's it for my list.
Hopefully one of those suggestions get added, and this post doesn't break any rules.
Goodbye.